In situ silicon and titanium nitride deposition

ABSTRACT

A method of processing semiconductor wafers is provided, comprising loading a batch of semiconductor wafers into a processing chamber; depositing titanium nitride (TiN) onto the wafers in the processing chamber; and depositing silicon onto the wafers in the processing chamber, without removing the wafers from the processing chamber between said depositing steps. In preferred embodiments, the TiN and silicon depositing steps are both conducted at temperatures within about 400-550° C., and at temperatures within 100° C. of one another.

FIELD OF THE INVENTION

The present application relates generally to semiconductor processing,and more particularly to silicon and titanium nitride deposition.

INCORPORATION BY REFERENCE

The present application incorporates by reference the full disclosuresof the following: U.S. Pat. No. 6,746,240; U.S. Pat. No. 6,962,859; U.S.Patent Application Publication No. 2003/0111013 A1; U.S. PatentApplication Publication No. 2004/0250853 A1; U.S. Patent ApplicationPublication No. 2005/0118837 A1; U.S. Patent Application Publication No.2006/0060137 A1; U.S. Patent Application Publication No. 2006/0088985A1; and Sze, VLSI TECHNOLOGY, pp. 240-41 (1988).

BACKGROUND

High-temperature ovens, called reactors, are used to create structuresof very fine dimensions, such as integrated circuits on semiconductorsubstrates. One or more substrates, such as silicon wafers, are placedon a substrate support inside the reaction chamber. Both the substrateand support are heated to a desired temperature. In a typical substratetreatment step, reactant gases (also referred to as precursors) arepassed over the heated substrate, causing the deposition (e.g., chemicalvapor deposition, or CVD) of a thin layer on the substrate. CVD istypically conducted at high temperatures, such as 250-900° C.

Deposition equipment normally includes a system for delivering gas tothe reaction chamber. The gas delivery system typically comprises aplurality of precursor sources, optionally one carrier gas and/or purgegas source, a network of pipes for delivering the precursor gases to thereaction chamber, eventually an injection manifold or showerhead forinjecting the gas evenly into the chamber, and a number of valves forcontrolling the gas flow. Also, some precursor sources may be in powderor liquid form, and means for vaporizing such precursors can be provided(e.g., bubblers).

Another type of deposition process is atomic layer deposition (ALD). InALD, two complementary precursors are alternatively introduced into thereaction chamber. Typically, a first precursor will adsorb onto thesubstrate surface, but it cannot completely decompose without the secondprecursor. The first precursor adsorbs until it saturates the substratesurface; further growth cannot occur until the second precursor isintroduced. Thus, the film thickness is controlled by the number ofprecursor injection cycles rather than the deposition time, as is thecase for conventional CVD processes. Accordingly, ALD allows forextremely precise control of film thickness and uniformity. ALD istypically conducted at temperatures in a range 250-500° C.

In ALD, the reaction chamber is typically pulsed with a non-reactiveprotective gas between injections of the two precursor gases, in anattempt to rid the chamber of any excess of the preceding precursor gas.Otherwise, the excess preceding precursor would intermix and react withthe subsequently pulsed precursor to form unwanted CVD-type growth onthe substrate surface and/or on surfaces of the chamber.

For various reasons, including low electrical resistivity, good thermalstability, and good diffusion barrier properties, there are numerousapplications for titanium nitride (TiN) in the fabrication of integratedcircuits. Exemplary applications include use as a contact or barrierlayer and as an electrode in electrical devices, such as transistors.

The properties of TiN, however, are closely dependent on processing anddeposition parameters. Thus, the suitability and desirability ofdeposited TiN for a particular application can depend on theavailability of a deposition process able to form TiN with desiredproperties, e.g., high uniformity and low resistivity. As a result,research into the development of new TiN deposition processes ison-going.

For example, the Low Pressure Chemical Vapor Deposition (LPCVD) of TiNfilms in a hot wall furnace has been described by N. Ramanuja et al. inMaterials Letters, Vol. 57 (2002), pp. 261-269. The reach of Ramanuja etal. is limited, however, as Ramanuja et al. investigated 100 mm wafers,rather than industry standard 200 mm and 300 mm wafers.

In addition to being able to form acceptable TiN films, it is desirablefor the deposition temperature of the TiN deposition process to berelatively low, thereby increasing flexibility for integrating thedeposition process with other processes and structures. For example,reducing deposition temperatures to the 400-500° C. range allows thefilms to be used in conjunction with multi-level aluminum or coppermetallization.

It has been found, however, that a reduction in the depositiontemperature results in the incorporation of significant amounts ofchlorine in the TiN film and results in a substantial increase inresistivity, which is undesirable. See J. T. Hillman, MicroelectronicEngineering, Vol. 19 (1992), pp. 375-378. To reduce the resistivity andthe chlorine content of the film, Hilman discloses a single waferdeposition process followed by a post-deposition anneal. Undesirably,however, such a process requires an additional process step and alsolimits throughput by using single wafer processing.

SUMMARY

It is an object and advantage of the present application to provideviable methods for in situ deposition of TiN and silicon onto substratesin a batch reactor.

In one aspect, a method of processing semiconductor wafers is provided.A batch of semiconductor wafers is loaded into a processing chamber.Titanium nitride (TiN) is deposited onto the wafers in the processingchamber. Silicon is deposited onto the wafers in the processing chamber,without removing the wafers from the processing chamber between saiddepositing steps.

In another aspect, an apparatus comprises a processing chamber, titaniumprecursor source, nitrogen precursor source, silicon precursor source,and valve system. The processing chamber is configured to contain aplurality of semiconductor wafers. The titanium, nitrogen, and siliconprecursor sources are each connected to the chamber to deliver a vaporof the titanium, nitrogen, and silicon precursor, respectively, into thechamber. The valve system is configured to allow selective control ofdelivery of the vapors into the chamber.

For purposes of summarizing the present application and the advantagesachieved over the prior art, certain objects and advantages have beendescribed herein above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

All of these embodiments are intended to be within the scope of theinvention. These and other embodiments of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description of the preferred embodiments having reference tothe attached figures, the invention not being limited to any particularpreferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIG. 1 is a flow chart illustrating a method of in situ deposition ofTiN and silicon onto substrates within a batch reactor.

FIG. 2 illustrates an exemplary furnace for use with embodiments of theinvention.

FIG. 3 illustrates an exemplary liquid delivery system for use withembodiments of the invention.

FIG. 4 illustrates another exemplary furnace for use with embodiments ofthe invention.

FIG. 5 illustrates an additional exemplary furnace for use withembodiments of the invention.

FIG. 6 is a schematic cross-sectional side view of an elongated batchprocess tube with a gas injector, constructed in accordance with oneembodiment of the invention.

FIG. 7 is a front view of a gas injector for use with the batch processtube of FIG. 6.

FIG. 8 is a horizontal cross-sectional view of the gas injector of FIG.7.

FIG. 9 is a reactant flow rate graph illustrating one method fordepositing TiN.

FIG. 10 is a reactant flow rate graph illustrating another method fordepositing TiN.

FIG. 11 is a reactant flow rate graph illustrating yet another methodfor depositing TiN.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Overview

It has recently been found that uniform and low resistivity TiN filmscan be economically deposited onto substrates in a batch reactor byperiodically introducing, or pulsing, one or more precursors into thereaction chamber of the reactor. For example, U.S. Patent ApplicationPublication No. 2006/0060137 A1 to Hasper et al. discloses forming TiNfilms using stable titanium and nitrogen precursors, i.e., precursorsthat are not radicals or a plasma. Hasper et al. disclose two generalmethods: (1) alternately pulsing a titanium precursor (such as titaniumtetrachloride, TiCl₄) and a nitrogen precursor (such as ammonia, NH₃)into the reaction chamber; and (2) continuously flowing one of theprecursors (such as NH₃) into the reaction chamber while pulsing theother precursor (such as TiCl₄). Hasper et al. found that these methodsallow for the deposition of TiN films with good uniformity and lowresistivity on industry size wafers, such as 200 mm or 300 mm wafers.Furthermore, Hasper et al. found that such methods allow for TiNdeposition at lower temperatures (e.g., between 450-600° C.), such thatthe deposition is compatible with other processes such as multi-levelaluminum or copper metallization.

A TiN film is susceptible to oxidation. Typically, a protectivepolysilicon capping film is deposited onto the TiN film shortly afterthe TiN film is deposited, to protect the TiN film from oxidation.Current methods involve depositing the TiN and the silicon capping filmin two different reactors, because silicon deposition is normallyconducted at temperatures that are significantly higher than thepreferred temperature range for depositing TiN (e.g., 450-500° C., astaught by U.S. Patent Application Publication No. 2006/0060137 A1 toHasper et al.). A primary reason why TiN and silicon have been depositedin separate reactors, as opposed to depositing both layers at differenttemperatures within the same reactor, is because changes in temperatureof a process tube used for depositing silicon (e.g., polysilicon) leadto unacceptable amounts of particle generation in the reaction chamber,which adversely affects the quality of deposited films. As wellunderstood, the deposition of silicon onto substrates in a reactionchamber also results in silicon deposition onto the reaction chamberwalls. It is usually the case that the deposited silicon and the chamberwalls have different coefficients of thermal expansion. For example,radiantly heated reaction chambers are typically formed of quartz walls,and the coefficients of thermal expansion of quartz and silicon are 0.59ppm/K and 2.3 ppm/K, respectively. If the temperature is variedsignificantly, the chamber walls and the silicon deposited thereon willexpand and contract at different rates. This causes silicon particles toflake off of the walls, thereby contaminating the chamber. For thisreason, it is generally not desirable to change the temperature in areaction chamber used for silicon deposition.

This problem also arises when TiN and silicon are deposited at differenttemperatures as adjacent layers on substrates. TiN has a coefficient ofthermal expansion of 9.3 ppm/K. Thus, if TiN is deposited at onetemperature (e.g., 450-500° C.) and silicon is deposited onto the TiN ata significantly higher temperature, there would be an unacceptable riskof flaking and particle generation caused by the differential in thermalexpansion and contraction of the silicon and the TiN.

Another reason why TiN and silicon have been deposited in separatereactors, as opposed to depositing both layers at different temperatureswithin the same reactor, is that it takes longer to wait for thetemperature to change and stabilize throughout the chamber (particularlyfor a batch reactor) than it takes to transfer the one or moresubstrates to another chamber maintained at a different temperature. Atthe relatively low temperature used for TiN deposition, heat transportthrough radiation is limited. Heat transport by conduction is also notvery efficient for a stack of substrates in a batch furnace at lowpressure. Consequently, temperature stabilization is slow, and it isoften less time consuming to transfer the substrates to another chamber.

The practice of depositing TiN and silicon in different reactorsinvolves several problems and drawbacks. The need to transfer substratesbetween two separate reactors involves greater equipment costs and morecomplicated processing, and results in lower throughput. Further, whiletransferring the substrate with the TiN film from the TiN depositionreactor to a silicon deposition reactor, the TiN becomes exposed to air,which leads to an undesirable interface between the TiN and the siliconcapping film.

Embodiments of the present application involve depositing a TiN film andan amorphous silicon capping film onto a plurality of substrates in asingle batch reactor in situ, without removing the substrates from theprocessing chamber between these deposition steps. By depositing bothfilms in the same reactor, it is possible to avoid the formation of anundesired interface between the TiN and the polysilicon capping film.The elimination of one reactor reduces costs. Also, the elimination ofthe intermediate substrate transfer step simplifies the processinglogistics and increases substrate throughput.

FIG. 1 illustrates the process. First, a plurality of substrates, suchas semiconductor wafers, is loaded 1 into a processing chamber of abatch reactor. TiN is deposited 2 onto the wafers in the processingchamber. Silicon is deposited 3 onto the wafers in the processingchamber, without removing the wafers from the processing chamber betweensaid depositing steps 2 and 3.

“Substrate” is used herein in its usual sense to include any underlyingsurface onto which a material is deposited or applied. Preferredsubstrates include semiconductor wafers, such as silicon wafers.However, substrates can be made of virtually any material, includingwithout limitation metal, silicon, germanium, plastic, and/or glass,preferably silicon compounds (including Si—O—C—H low dielectric constantfilms) and silicon alloys. Substrates can also have in them physicalstructures such as trenches or steps, as in a partially fabricatedintegrated circuit.

In some embodiments, the TiN deposition is conducted in accordance withthe aforementioned methods taught by U.S. Patent Application PublicationNo. 2006/0060137 A1 to Hasper et al.: (1) alternately pulsing a titaniumprecursor (such as TiCl₄) and a nitrogen precursor (such as NH₃) intothe reaction chamber, preferably with purge or evacuation stepstherebetween; and (2) continuously flowing one of the precursors (suchas NH₃) into the reaction chamber while pulsing the other precursor(such as TiCl₄). In other embodiments, the TiN deposition involves thefollowing cyclical sequence: substantially simultaneous pulses of thetitanium and nitrogen precursors, a purge or evacuation step, anothernitrogen precursor pulse (referred to elsewhere herein as a “flush”),and then another purge or evacuation step. In some embodiments, both theTiN deposition and the polysilicon deposition are conducted at arelatively low temperature (e.g., 300-600° C., more preferably 400-500°C.). In preferred embodiments, trisilane (Si₃H₈) is used as a siliconprecursor.

While the above discussion contemplates the in situ deposition ofsilicon capping films onto TiN films, in some embodiments the depositionsequence of the films is reversed, such that TiN films are deposited insitu onto previously deposited silicon films. For example, in FIG. 1,the silicon deposition 3 can occur before the TiN deposition 2.

Batch Reactor

As mentioned above, the in situ deposition of TiN and silicon films ispreferably conducted on a plurality of substrates, such as semiconductorwafers, in a batch reactor. Several exemplary batch reactors are nowdescribed.

Preferably, the batch reactor is configured or programmed to deliver oneor more precursors in temporally separated pulses. The batch reactorpreferably has a vertically extending reaction chamber that accommodatessubstrates vertically separated from each other, with major faces of thesubstrates oriented horizontally. Preferably, the reaction chamberaccommodates at least 25 substrates, and more preferably at least 50substrates.

FIG. 2 schematically shows a vertical furnace reactor 10 thataccommodates substrates 40 vertically separated from one another, andwhich has benefits for efficient heating and loading sequences. Thefurnace 10 is preferably adapted to support 100-125 substrates. Examplesof suitable vertical furnaces are the A400™ and A412™ vertical furnaces,commercially available from ASM International, N.V. of Bilthoven, theNetherlands. A vertical furnace type of reactor has benefits forefficient heating and loading sequences. It will be understood, however,that while preferred embodiments are presented in the context of avertical batch furnace, the principles and advantages disclosed hereinwill have application to other types of reactors. For example, while theillustrated reactors are shown holding substrates in avertically-separated manner, the methods described herein can be appliedto a batch reactor that holds substrates in a horizontally separatedmanner.

With continued reference to FIG. 2, a tube 12 defines a reaction chamber20 in the interior of the vertical furnace or reactor 10. The lower endof the tube 12 terminates in a flange 90, which mechanically seals thechamber 20 by contact with a lower support surface 14. Process gases canbe fed into the reaction chamber 20 through a gas inlet 22 at the top ofthe chamber 20 and evacuated out of the chamber 20 through a gas outlet24 at the bottom of the chamber 20. The reaction chamber 20 accommodatesa wafer boat 30 holding a stack of vertically spaced substrates orwafers 40.

The process tube flange 90 can be maintained at an elevated temperatureto avoid condensation of process gases on it. It will be appreciatedthat the elevated temperature can vary from process to process and ispreferably chosen based upon the identities of the process gases (which,in some embodiments, are TiCl₄, NH₃, Si₃H₈, and N₂). For example, theelevated temperature of the flange 90 is preferably above 120° C.,preferably about 180-200° C. Regulation of the temperature of the flange90 can be achieved by providing it with electrical heaters and awater-cooling system. The water-cooling is desired primarily to avoidoverheating of the flange 90 during unloading of a batch of hot wafers40.

Various systems can be used to supply reactants or precursors to thereaction chamber 20 (FIG. 2). For example, where the precursor is a gas,it can be flowed directly from a gas source to the chamber 20. Thetiming and rate of the flow of the gas can be controlled by, e.g., massflow controllers, as known in the art.

Where the precursor, such as TiCl₄, is stored as a liquid, a bubbler canbe used to supply the precursor to the chamber 20 in gaseous form. Thetiming and rate of flow of such a precursor can be regulated bycontrolling the flow of carrier gas through the liquid in the bubblerand by controlling the temperature of the liquid. It will be appreciatedthat the quantity of the liquid precursor carried by the carrier gasincreases with increasing temperature.

FIG. 3 schematically shows an exemplary system for controlling the flowof liquid precursors, such as TiCl₄. The liquid precursor is stored in acontainer 50. Liquid flow control is used to regulate the amount of theliquid precursor flowing into the reactor 10 by regulating the flow ofthe liquid into an evaporator or vaporizer 60. After being vaporized,well-separated pulses of a precursor can be generated and flowed intothe reaction chamber 20 using a valve system 70 comprising valves 80,shown in the upper section of FIG. 3. Preferably, the valves 80 of thevalve system 70 are operated at elevated temperatures and have no orminimal dead volume, to provide good separation between the flow ofdifferent reactants. Such a valve system is described in further detailin U.S. Patent Application Publication No. 2004/0250853 A1.

As noted above, process gases can be introduced into the chamber 20 invarious ways. For example, in the reactor illustrated in FIG. 2, allgases are introduced into the interior 20 of the reactor 10 at the top,via the top inlet 22, and exhausted at the bottom of the reactor 10, viathe exhaust 24. In other embodiments, a more even distribution of theprocess gases can be achieved over the length of the tube by usingmultiple-hole injectors for introduction of process gases into thereactor. Suitable multiple-hole injectors are disclosed in U.S. Pat. No.6,746,240, and U.S. Patent Application Publication No. 2003/0111013 A1.Alternatively, less spacious and cylindrical multiple-hole injectors canbe used. Such injectors can have, e.g., a diameter of about 25 mm andholes of about 1 mm diameter. In some preferred embodiments,multiple-hole injectors are preferably mounted on or beneath the flange90 at the lower end of the reaction chamber 20 and point upwardly.

A multiple-hole injector is preferably not used to introduce a purgegas, however, because the top part of the reaction chamber 20 may be noteffectively purged by an injector that only extends part way up theheight of the chamber 20. Preferably, a purge gas is introduced into thechamber 20 at the chamber end that is opposite to the exhaust end, sothat the purge gas flows through all regions of the reaction chamber 20after entry and before being exhausted.

FIG. 4 shows another exemplary batch reactor. In this design, theprocess tube 100 is closed at the top. An advantage of this design isthat the process tube 100 is simpler in construction and eventualproblems with the gas-tightness and the thermal isolation of the topinlet 22 (FIG. 2) can be prevented. All gases in this set-up areintroduced through gas injectors 110, of which two are shown.Preferably, separate injectors 110 are used for each gas. In the case ofTiN deposition, one injector 110 can be used for each of the titaniumprecursor gas (such as TiCl₄) and the nitrogen precursor gas (such asNH₃). An additional injector 110 can be provided for the siliconprecursor gas (such as Si₃H₈). These injectors 110 are preferablymultiple-hole gas injectors having holes distributed over the height ofthe tube 100. The injectors 110 may be each oriented substantiallyperpendicular to the substrates. Each injector 110 may extend along amajority of a length of the arrangement of substrates. An exhaust 24 isprovided, preferably at the bottom of the tube 100, for process gasesexiting the tube 100.

An additional injector 110 can be used for a purge gas, preferably aninert gas such as nitrogen gas. The injector 110 for the purge gas ispreferably a tube with an open end at the top and without gas dischargeholes in its sidewall, so that all the purge gas is discharged at thetop of the reaction chamber 120. FIG. 5 illustrates a reactor 10 havingthree vertically extending injectors, 110 a, 110 b and 110 c. Theinjectors 110 a, 110 b and 110 c each have an inlet 140 a, 140 b, and140 c, respectively, for connecting to one or more gas feeds. Theinjector 110 b opens at its top end 112 to allow purge gas to flowdownward through the reactor 10 and to exit out the exhaust 24 at thebottom of the reactor 10. In other embodiments, the exhaust 24 can be atthe top of the reaction chamber 120 and the purge gas can be dischargedat the bottom of the reaction chamber 120. Advantageously, using suchmultiple-hole gas injectors, the evenness of gas distribution into thereaction chamber can be improved, thereby improving the uniformity ofdeposition results.

FIGS. 6-8 illustrate another version of an exemplary batch reactor, alsocommercially available under the trade name Advance 412™ or A412™ fromASM International N.V. of Bilthoven, The Netherlands. FIG. 6 is aschematic cross-sectional side-view of the elongated furnace with a gasinjector. The process tube or chamber 526 is preferably surrounded by aheating element (not shown). A liner 528, delimiting the outer perimeterof the reaction space 529, is preferably provided inside the processchamber 526. Preferably, at the bottom of the process chamber 526, awafer load 550 may enter and exit the process chamber 526 by a door 530.Precursor source gas is injected through a gas injector 540, preferablyvia a gas feed conduit 544. The gas injector 540 is provided with apattern of holes 548, preferably extending substantially over the heightof the wafer load 550. Note that, because gases are first introducedinto the reaction space 529 from the holes 548 of the gas injector 540,the interior of gas delivery devices through which gases travel, such asthe gas injector 540, is not part of the reaction space 529 and is, in asense, outside of the reaction space 529. Consequently, the reactionspace 529 comprises the interior volume of the process chamber 526,excluding the volume occupied by gas delivery devices such as the gasinjector 540. Further details of the chamber 526 are provided in U.S.Patent Application Publication No. 2003/0111013 A1.

In a preferred embodiment, inside the process chamber 526, gas is flowedin a generally upward direction 552 and then removed from the reactionspace 529 via an exhaust space 554 between the process chamber 526 andthe liner 528, where gas flows in a downward direction 556 to theexhaust 558, which may be connected to a pump (not shown). The gasinjector 540 preferably distributes process gases inside the processchamber 526 over the entire height of the reaction space 529. The gasinjector 540 itself acts as a restriction on the flow of gas, such thatthe holes 548 that are closer to the conduit 544 tend to inject more gasinto the reaction space than those holes 548 that are farther from theconduit 544. Preferably, this tendency for differences in gas flowsthrough the holes 548 can be compensated to an extent by reducing thedistance between the holes 548 (i.e., increasing the density of theholes 548) as they are located farther away from the conduit 544. Inother embodiments, the size of individual holes making up the holes 548can increase with increasing distance from the conduit 544, or both thesize of the holes 548 can increase and also the distance between theholes 548 can decrease with increasing distance from the conduit 544.Advantageously, however, the preferred embodiments are illustrated withholes 548 of constant size so as to minimize the surface area of thesides of the gas injector 540 containing the holes 548.

The injector 540 is advantageously designed to reduce the pressureinside the gas injector, resulting in a reduction of the gas phasereactions within the injector, since reaction rates typically increasewith increasing pressure. While such reduced pressure can also lead to apoor distribution of gas over the height of the gas injector 540, thedistribution of holes 548 across the height of the injector 540 isselected to improve uniformity of gas distribution.

FIG. 7 shows one illustrative embodiment of the gas injector 540. Thegas injector 540 preferably comprises two gas injector parts 541 and542, each preferably provided with separate gas feed conduit connections545 and 546, respectively. The first part 541 injects gas into the lowervolume of the reaction space 529 (FIG. 6) and the second part 542injects gas into the upper volume of the reaction space 529. The parts541 and 542 are connected by linkages 549 and 551. At its top end, thegas injector 540 can be provided with a hook 553, to secure the top endof the gas injector 540 to a hook support inside the chamber 526 (FIG.6).

The gas injector 540 is provided with a pattern of holes 548substantially extending over the height 560 (FIG. 6) of the wafer load550. The total cross section of the holes is preferably at least about30 mm². The diameter of each of holes 548 is preferably about 1 mm ormore, more preferably between about 2.5 mm and 3.5 mm, and in oneembodiment about 3 mm. In the illustrative embodiment shown in FIG. 7,the gas injector 540 has a total of 40 holes 548 for a total holecross-sectional area of about 282 mm². More generally, the totalcross-sectional area of the holes 548 is preferably about 30 mm² ormore, and more preferably between about 196 mm² and 385 mm².

With reference to FIG. 8, each part 541 and 542 of the gas injector 540has an inner cross-sectional area 564 and 562, respectively, availablefor the conduction of source gases through the gas injector 540.Preferably, each of inner cross-sectional areas 564 and 562 are at leastabout 100 mm². In the illustrated embodiment, the cross-sectional areaof each of the parts 541, 542 of the gas injector 540 is about 330 mm².More generally, the cross-sectional area of each of the parts 541, 542is preferably between about 140 mm² and 600 mm², more preferably betweenabout 225 mm² and 455 mm².

The cross-section shown in FIG. 8 is taken through the lower end of thegas injector 540 and straight through a pair of injection holes 548provided in gas injector part 541, for injecting the gas into the lowerend of the process chamber 526. Preferably, in each gas injector part,the holes 548 are provided in pairs, at the same height. In addition,the two holes 548 preferably inject the precursor gas in two directions566 and 568 forming an angle 570 of between about 60 and 120 degrees,illustrated at about 90 degrees, to improve the radial uniformity.Moreover, as shown, the tubes comprising the gas injector 540 preferablyhave an oblong shape, as viewed in horizontal cross-section. Preferably,the longer dimension of the oblong shape faces the center of the processchamber 526, i.e., the side of the oblong shape with the longerdimension is perpendicular to an imaginary line extending radially fromthe center of the process chamber 526.

In a preferred embodiment, in a CVD mode, two precursor source gases,providing the two constituting elements of a binary film, are mixed inthe gas supply system (not shown) prior to entering the gas injector 540via feed conduit connections 545 and 546 (FIG. 7). Pre-mixing theprecursor gases in the gas supply system is one way to ensure ahomogeneous composition of injected gas over the height of the boat.However, the gases can be flowed into the process chamber 526 (FIG. 6)without pre-mixing. In another embodiment, the two precursor sourcegases can each be injected via their own separate gas injectors 540 (notshown), so that they are first mixed after being injected into thereaction space 529. Consequently, it will be appreciated that more thanone gas injector 540 may be located inside the process chamber 526.

Advantageously, the use of two gas injector parts 541 and 542 allows forfurther tuning possibilities. The flows supplied to the different gasinjector parts 541, 542 can be chosen differently to fine-tune the gasflow into the reaction space 529. This will improve uniformity in thedeposition rates of precursors over the height 560 of the wafer load 550(FIG. 6).

One skilled in the art will appreciate that further modifications to thebatch reactor, or to the way of operating the batch reactor, known inthe art, can be applied to improve the performance of this process. Forexample, it is possible to use a holder boat or ring boat (i.e., a waferboat in which each wafer is individually supported by a separate waferholder or ring-shaped holder inserted into the boat).

It will be appreciated that while the aforementioned hardwareconfigurations are described in the context of pulsed CVD and ALD, theyare equally suitable for use in the context of low pressure chemicalvapor deposition (LPCVD).

TiN Deposition

It has been found that uniform and low resistivity TiN films can bedeposited on wafers in a batch reactor by periodically introducing, orpulsing, one or more precursors into the reaction chamber of thereactor. Preferably, the TiN films are formed using stable titanium andnitrogen precursors, i.e., precursors which are not radicals or aplasma. More preferably, titanium tetrachloride (TiCl₄) and ammonia(NH₃) are used as the titanium and nitrogen precursors, respectively.

In one method, both precursors (e.g., TiCl₄ and NH₃) are alternatelypulsed into the reaction chamber, preferably with intermediate purge gasinjections or chamber evacuation steps. In this method (described belowwith reference to FIG. 9), each pair of pulses comprises one cycle, andany number of cycles can be conducted. In another method (describedbelow with reference to FIG. 10), only one precursor is pulsed while theother precursor flows continuously into the reaction chamber. In somepreferred embodiments, the titanium precursor, e.g., TiCl₄, is pulsedinto the reaction chamber while the nitrogen precursor, e.g., NH₃, isflowed continuously into the chamber. In still another method (describedbelow with reference to FIG. 11), each cycle includes, in the followingsequence, substantially simultaneous pulses of the titanium and nitrogenprecursors, a purge or evacuation step, another nitrogen precursor pulse(also referred to as a “flush”), and then another purge or evacuationstep. The second nitrogen precursor pulse or flush is provided to morefully react nitrogen with any remaining titanium from the prior titaniumpulse.

The TiN deposition advantageously can be performed at a temperature ofless than about 600° C. and, more preferably, at less than about 500°C., e.g., about 450-500° C. Thus, the deposition is compatible withother processes such as multi-level aluminum or copper metallization. Inaddition, the deposition can advantageously be used to deposit films onindustry standard 200 mm and 300 mm wafers.

In some preferred embodiments, a stack of vertically-spaced substrates,e.g., semiconductors wafers, is accommodated in a batch reaction chamberand temporally separated pulses of the titanium and nitrogen precursors,such as TiCl₄ and NH₃, are supplied to the reaction chamberalternatingly and sequentially in an ALD of TiN. FIG. 9 is a reactantflow rate graph illustrating an embodiment of this method for alternatepulses of TiCl₄ and NH₃. While not shown, it will be understood thatchamber purge or evacuation steps can be conducted during time intervalsbetween the alternate pulses of the reactants. In FIG. 9, the TiCl₄ andNH₃ flows are shown separately for clarity. The cycling sequencepreferably ends with a nitrogen precursor gas (e.g., NH₃) pulse. Inother words, after the last TiCl₄ pulse, an additional NH₃ pulse ispreferably injected, which is not followed by another TiCl₄ pulse.

The deposition rate of the TiN has been found to be particularlysensitive to variations in the gas partial pressure of NH₃. As a result,NH₃ is preferably flowed into the chamber using a gas injector havingvertically distributed holes to allow an even distribution of the NH₃.Preferably, each reactant is removed, e.g., by purging with an inert gasor evacuating the reaction chamber, before introduction of the otherreactant. The duration of each of the pulses is preferably about 60seconds or less, more preferably about 30 seconds or less, and even morepreferably about 15 seconds or less.

When TiN films are formed by continuous CVD, by continuously flowingTiCl₄ and NH₃ into a reaction, the deposition rate of the TiN films hasbeen found to not vary significantly with the partial pressure of theTiCl₄. On the other hand, the deposition rate has been found to beapproximately proportional to the partial pressure of the NH₃. Fordepositing uniform films, these findings indicate that the mode ofintroduction and distribution of NH₃ inside the reaction chamber is moreimportant than that for TiCl₄, whether or not NH₃ is pulsed into thechamber, e.g., whether or not NH₃ is used in an ALD or pulsed CVDprocess. As a result, as noted above, NH₃ is preferably discharged intothe reaction chamber in a manner that maximizes the evenness of thedistribution of the gas into the chamber. In particular, NH₃ ispreferably discharged into the vertical furnace reaction chamber in avertically distributed manner, e.g., through a multiple-hole injectorhaving a plurality of vertically spaced apart holes, such as thosediscussed above. The injector preferably extends substantially over aheight of the chamber, such that the holes of the injector span most orall of the vertical height occupied by the substrates. TiCl₄ can also bedischarged using the multiple-hole injector, or it can be discharged ata feed end of the reaction chamber (FIG. 2).

In other preferred embodiments, the nitrogen precursor, e.g., NH₃, iscontinuously supplied to the reaction chamber and only the titaniumprecursor, e.g., TiCl₄, is supplied pulse-wise, resulting in CVD of TiN.FIG. 10 is a reactant flow rate graph illustrating an embodiment of thismethod for pulsed flow of TiCl₄ and continuous flow of NH₃. In FIG. 10,the TiCl₄ and NH₃ flows are superimposed for a better understanding ofrelative flow rate value. Advantageously, such a deposition schemeallows an increased deposition rate per reactant pulse without losingfilm quality, in comparison to a scheme in which both TiCl₄ and NH₃ arealternately pulsed. By continuously flowing one precursor, more than onemonolayer of TiN is typically deposited per TiCl₄ pulse. In addition,where the titanium precursor pulses are relatively short, the depositedtitanium-containing films are effectively nitrided by the nitrogenprecursor flow between the titanium precursor pulses. Thus, highquality, low resistivity and uniform TiN films can be obtained atrelatively low deposition temperatures of preferably less than about600° C., and, more preferably, less than about 500° C., e.g., about 450°C. Preferably, the pulse duration is about 60 seconds or less, morepreferably, about 30 seconds or less and, most preferably, about 15seconds or less.

In still other preferred embodiments, each deposition cycle includes, inthe following sequence, substantially simultaneous pulses of thetitanium and nitrogen precursors, a purge or evacuation step, anothernitrogen precursor pulse, and then another purge or evacuation step.FIG. 11 is a reactant flow rate graph illustrating an embodiment of thismethod for pulses of TiCl₄ and NH₃. FIG. 11 shows the TiCl₄ and NH₃flows separately for clarity. In this embodiment, TiCl₄ pulses 200 occursubstantially simultaneously with NH₃ pulses 210. However, an additionalNH₃ pulse 220 (also referred to as an “ammonia flush”) occurs temporallybetween the combined or simultaneous pulses 200, 210. While not shown,it will be understood that a chamber purge or evacuation step can beconducted after the combined pulse 200, 210 and before the ammonia flush220. In addition, another chamber purge or evacuation step can beconducted after the ammonia flush 220 and before the next combined pulse200, 210. In other words, if the pulses 200 and 210 occur during a firsttime interval of the deposition cycle, and if the pulse 220 occursduring a second time interval of the cycle, then the purge or evacuationsteps can be conducted between the first and second time intervals andagain after the second time interval.

Advantageously, high quality titanium nitride films can be formed inaccordance with the preferred embodiments. For example, the thicknessesof deposited titanium nitride films can vary by less than about 3 nmbetween substrates in a batch of substrates, and the resistivity canvary by less than about 5 μOhm·cm. Moreover, the films can be formedhaving a low resisitivity of about 220 μOhm·cm or less.

Advantageously, at lower deposition temperatures (e.g., 450° C.), theaverage film thickness across a wafer has been found to be exceptionallyuniform from wafer to wafer, varying less than about 3 nm among thevarious wafers of a batch of wafers. At this temperature, the averageresistivity of the films has been found to be advantageously uniform,varying less than about 5 μOhm·cm among the various wafers in the batch.

It is understood that precursor pulse time affects film thickness andresistivity. While longer pulse times would be expected to increase orpossibly not affect the thickness of the deposited film in cases wherethe total TiCl₄ exposure time was unchanged, it has been unexpectedlyfound that pulse times longer than about 30 seconds actually cause adecrease in average film thickness (in some experiments, from about 23.5nm to about 23 nm). Even more unexpectedly, the average resistivity ofthe deposited film has been found to be strongly dependent on pulsetimes. In particular, in some experiments, film resistivity has beenfound to increase from about 220 μOhm·cm for TiCl₄ pulse durations ofabout 15 seconds to about 520 μOhm·cm for TiCl₄ pulse durations of about60 seconds. Thus, shorter pulse times advantageously allow deposition ofTiN films with reduced resistivity, e.g., about 220 μOhm·cm or less.

Where both reactants are pulsed, it will be appreciated that pulse timesfor both reactants can be the same or each can have a different pulseduration. Moreover, whether one or both reactants are pulsed, theduration of the pulses can remain the same throughout a deposition, orcan vary over the course of the deposition.

In addition, the cycle duration can be selected to give a desired TiNfilm resistivity. For example, resistivities of about 520 μOhm·cm toabout 220 μOhm·cm can be achieved by appropriately adjusting the TiCl₄pulse time (e.g., between about 15-60 seconds), or the duration of eachcycle of process gases can be adjusted (e.g., between about 1-10minutes).

Silicon Deposition

As discussed above, a silicon layer can be deposited onto the wafers inthe batch reactor either before or after the TiN layer is deposited. Thesilicon layer may comprise amorphous silicon, and may be deposited byCVD, preferably at a low temperature or a temperature that is the sameas or relatively close to the temperature at which the TiN layer isdeposited. The deposited silicon and TiN layers can be deposited indirect contact with one another (e.g., immediately adjacent). Thesilicon layer may be deposited over the TiN layer so as to be aprotective capping film. Alternatively, the TiN layer can be depositedover the silicon layer.

Between the steps of TiN deposition and silicon deposition, any excessprecursor of associated with the earlier-deposited layer can be removedfrom the chamber by the injection of a purge gas, by a chamberevacuation process, by displacement of the earlier precursor gas by agas carrying a reactive species, or any combination thereof. Where theearlier precursor gas is removed by purging, the process chamber ispreferably purged for a duration long enough to replace the atmospherein the chamber at least once.

A silane is preferably used as the silicon precursor. The silane can beselected from the group consisting of monosilane (SiH₄), a polysilaneand a chlorosilane (SiH_(4-n)Cl_(n), where n=1 to 4). More preferably, apolysilane is used as the silicon precursor to form the silicon layer,discussed below. As used herein, a “polysilane” has the chemical formulaSi_(n)H_(2n+2), where n=2 to 4. Preferably, the polysilane is disilaneor trisilane. Most preferably, the polysilane is trisilane.Consequently, while embodiments of the invention are described in thecontext of employing CVD cycles with trisilane, the skilled artisan willappreciate, in view of the present disclosure, that certain advantagesof the described processes can be obtained with other precursors and/orother deposition techniques.

Trisilane (H₃SiSiH₂SiH₃ or Si₃H₈) offers substantial benefits when usedas a silicon precursor, as disclosed in U.S. Patent ApplicationPublication No. 2005/0118837 A1 and U.S. Pat. No. 6,962,859. Forexample, films can be deposited with trisilane at substantially lowertemperatures than with other silicon precursors, such as silane (SiH₄),which advantageously makes possible in situ deposition of both TiN andsilicon in a low temperature range (e.g., 400-500° C.). Moreover,deposition rates with trisilane are relatively insensitive to substratematerial and thickness. Also, trisilane has an extremely short filmnucleation time, which reduces the size of localized crystallinedeposits of silicon. As a result, deposited silicon films can be madethinner, while still being uniform. Moreover, the films will showreduced surface roughness due to the reduced size of the localizedsilicon deposits. In addition, with regards to process throughput,trisilane exhibits higher deposition rates relative to silane. Trisilanealso reduces thermal budgets, since it allows use of lower processtemperatures than does silane.

Thus, employing trisilane in the deposition methods described hereinprovides numerous advantages. For example, these deposition methodsenable in situ deposition of TiN and silicon layers in a single reactionchamber. These methods also enable the production of silicon-containingcompound films that are uniformly thin and continuous. These advantages,in turn, enable devices to be produced in higher yields, and also enablethe production of new devices having smaller circuit dimensions and/orhigher reliability.

The silicon precursor is preferably introduced into the process chamberin the form of a feed gas or as a component of a feed gas. The feed gascan include gases other than the silicon precursor, such as inertcarrier gases. The carrier gas can comprise carrier gases known in theart, such as nitrogen, hydrogen, helium, argon, or various combinationsthereof. Where the silicon precursor is trisilane, the trisilane ispreferably introduced into the chamber by way of a bubbler used with acarrier gas to entrain trisilane vapor. More preferably, a temperaturecontrolled bubbler is utilized.

In forming the silicon layer, deposition from a silicon precursor can beconducted according to various deposition methods known to those skilledin the art, but the greatest benefits are obtained when deposition isconducted according to the CVD methods taught herein. The disclosedmethods can be practiced by employing CVD, including plasma-enhancedchemical vapor deposition (PECVD) or, more preferably, thermal CVD.

Deposition conditions are preferably tailored to processing in theparticular type of reactor in which substrates are loaded. In general,deposition conditions are established to supply sufficient energy topyrollize or decompose the silicon precursor on a hot substrate surface.

In addition, deposition conditions are preferably established so thatthe reaction rate of the silicon precursor is the limiting variable forthe silicon deposition rate. Thus, the ability of hot wall reactors toachieve highly uniform temperature distributions can advantageously beapplied to form uniform layers. While depositions conducted underreaction kinetics limited conditions have deposition rates that aresensitive to temperature changes, the ability to establish hightemperature uniformity minimizes the effect of this sensitivity.Moreover, reaction kinetics limited conditions advantageously havedeposition rates that are relatively insensitive to supplied reactantconcentrations.

It will be appreciated that a reaction kinetics limited regime isprimarily achieved by use of a relatively low temperature. This resultsin a reduced film deposition rate that is preferable in a batch furnace.Because of the large batch size, an adequate throughput can still beachieved at a deposition rate that results from temperatures shifteddown into the reaction rate limited regime. Advantageously, trisilaneenables acceptable deposition rates at very low temperatures, allowing aconsiderably reduced consumption of thermal budgets. As the skilledartisan will readily appreciate, thermal budgets are constantly reducedas critical dimensions are scaled down, tolerances for diffusion arereduced, and new materials with lower resistance to thermal processingare introduced. The silicon deposition process is preferably operated ata temperature below about 600° C., more preferably below about 525° C.,more preferably below about 500° C., more preferably below about 475° C.The silicon can be deposited at a temperature between about 300° C. andabout 500° C.

In addition to temperature, the skilled artisan will appreciate that thekinetic regime is partially dependent upon the reactant supply orpartial pressure of the silicon precursor. Preferably, the reaction rateis slower than the rate at which reactant is supplied.

The thickness of the deposited silicon film can be varied according tothe intended application, as known in the art, by varying the depositiontime and/or gas flow rates for a given set of deposition parameters(e.g., total pressure and temperature).

A silicon layer is first deposited by flowing a silicon precursor,preferably trisilane. As noted, process conditions are preferablyarranged for deposition in the kinetic regime. The process is preferablyoperated at a temperature below about 600° C. and, more preferably, at atemperature below about 500° C., and, even more preferably, at atemperature between about 400-450° C. In addition, the reactant supplyor partial pressure of trisilane is preferably set at a sufficiently lowlevel to maintain the deposition in the kinetic regime. As long as thereaction rate is slower than the rate at which reactant is supplied,uniformity in a properly tuned batch furnace (in which uniformtemperatures can be maintained) is excellent. Reference is made to Sze,VLSI TECHNOLOGY, pp. 240-41 (1988). In the illustrated batch reactors,process pressure is maintained at about 10 Torr or below and morepreferably about 1 Torr or below. In order to maintain reaction ratelimited deposition, trisilane preferably is supplied at less than about100 sccm trisilane, and, more preferably, at less than about 20 sccm.The trisilane is typically diluted with a flow of a non-reactive orinert gas such as N₂, H₂, Ar or He. The trisilane partial pressure isthus preferably below about 10 mTorr, more preferably, about 3-4 mTorr.Preferably, a trisilane deposition step has a duration of about 30-120seconds.

In addition, the silicon deposition and the TiN deposition (describedabove) are preferably conducted under generally isothermal conditions.In other words, if the TiN deposition is conducted at a first averagetemperature and the silicon deposition is conducted at a second averagetemperature, then the first and second temperatures differ, if at all,by preferably less than 100° C., more preferably less than 50° C., andeven more preferably less than 20° C. An “average temperature” refers toa time-averaged temperature, reflecting the possibility that temperaturemay fluctuate during a deposition process. Conducting the silicondeposition and TiN deposition at the same or similar averagetemperatures simplifies processing because there is no need tosignificantly adjust temperature between deposition steps, or totransfer the substrates to a different reactor. In one embodiment, theTiN and silicon depositing steps are both conducted at temperatureswithin about 400-550° C., and more preferably within about 450-500° C.

Advantageously, the above-described in situ deposition of TiN andsilicon within a relatively narrow temperature range can be conductedwithout producing an undesirable amount of particle generation. Asdescribed above, a chamber used for in situ processes at significantlydifferent temperatures results in unacceptable particle generation whenone of the processes is silicon deposition, due in large part to thedifferential in thermal expansion and contraction between the siliconand the other parts of the reaction chamber, such as the chamber walls.Silicon and TiN also have significantly different rates of thermalexpansion and contraction, exacerbating the problem for adjacent TiN andsilicon layers. However, the presently disclosed embodimentssubstantially overcome this problem, due to the relatively narrowtemperature range within which the TiN and silicon layers are deposited.

EXAMPLE

The following represents process conditions in one example of in situdeposition of TiN and amorphous silicon layers onto a plurality ofsemiconductors in a batch reaction chamber. For pulsed CVD TiNdeposition, temperature in the reaction chamber can be about 450° C.,and pressure can be about 200 mTorr. The titanium precursor can beTiCl₄, and the nitrogen precursor can be NH₃. The TiCl₄ can be deliveredto the chamber via an N₂ carrier gas. The flow rate of TiCl₄ during theTiCl₄ pulses can be about 1.5 g/min, and the flow rate of the N₂ carriergas can be about 200 sccm. The flow rate of the NH₃ during depositioncan be about 0.19 slm. The duration of the TiCl₄ pulses can be 15seconds, 30 seconds, or 60 seconds.

As discussed above, the TiN deposition can be conducted in three ways:(1) alternately pulsing the TiCl₄ and NH₃ precursors into the reactionchamber, preferably with purge or evacuation steps therebetween; (2)continuously flowing one of the precursors (such as NH₃) into thereaction chamber while pulsing the other precursor (such as TiCl₄); and(3) repeating the following cycle: substantially simultaneous pulses ofTiCl₄ and NH₃, a purge or evacuation step, another NH₃ pulse (also knownas an “ammonia flush”), and then another purge or evacuation step. TheNH₃ flow during the ammonia flush can be about 1 slm.

A capping film of amorphous silicon can be deposited in situ onto theTiN layer. The temperature and pressure of the reaction chamber can bemaintained at about 450° C. and about 200 mTorr, respectively. Trisilanecan be continuously injected into the chamber at a flow rate of about 60sccm, with an N₂ carrier gas flow rate of about 1 slm.

Accordingly, it will be appreciated by those skilled in the art thatvarious other omissions, additions and modifications may be made to themethods and structures described above without departing from the scopeof the invention. All such modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

1. A method of processing semiconductor wafers, comprising: loading abatch of semiconductor wafers into a processing chamber; depositingtitanium nitride (TiN) onto the wafers in the processing chamber; anddepositing silicon onto the wafers in the processing chamber, withoutremoving the wafers from the processing chamber between said depositingsteps.
 2. The method of claim 1, wherein said step of depositing siliconoccurs after said step of depositing TiN.
 3. The method of claim 1,wherein said step of depositing TiN occurs after said step of depositingsilicon.
 4. The method of claim 1, wherein the TiN depositing step isconducted at a first average temperature and the silicon depositing stepis conducted at a second average temperature, the first and secondtemperatures being within 100° C. of one another.
 5. The method of claim4, wherein the first and second temperatures are within 50° C. of oneanother.
 6. The method of claim 1, wherein the TiN and silicondepositing steps are both conducted at temperatures within about400-550° C.
 7. The method of claim 6, wherein the TiN and silicondepositing steps are both conducted at temperatures within about450-500° C.
 8. The method of claim 1, wherein depositing siliconcomprises flowing trisilane through the processing chamber.
 9. Themethod of claim 1, wherein loading the batch of wafers comprisesproviding an arrangement of generally parallel wafers spaced from oneanother, and wherein depositing TiN and silicon comprises flowingprecursor gases through gas injector tubes each positioned within theprocessing chamber and oriented substantially perpendicular to thewafers, each injector tube extending along a majority of a length of thearrangement of wafers, each tube having a plurality of gas injectorholes along its length.
 10. The method of claim 9, wherein loading thebatch of wafers comprises providing an arrangement of generallyhorizontal wafers spaced vertically from one another, each injector tubebeing oriented substantially vertically and extending along a majorityof a height of the arrangement of wafers.
 11. The method of claim 9,wherein depositing TiN comprises: flowing a plurality of separate pulsesof a titanium precursor gas through a first of the injector tubes; andflowing a plurality of separate pulses of a nitrogen precursor gasthrough a second of the injector tubes, each of the nitrogen precursorgas pulses occurring temporally between two successive ones of thetitanium precursor gas pulses.
 12. The method of claim 11, whereindepositing TiN further comprises, during each of a plurality of separatetime intervals, one of (1) flowing a purge gas into the processingchamber and (2) evacuating the processing chamber, each said timeinterval being after a pulse of one of the precursor gases and before animmediately following pulse of the other of the precursor gases.
 13. Themethod of claim 11, wherein depositing TiN further comprises flowing anadditional pulse of the nitrogen precursor gas through the secondinjector tube after a last of the titanium precursor gas pulses, saidadditional nitrogen precursor gas pulse not being followed by anothertitanium precursor gas pulse.
 14. The method of claim 9, whereindepositing TiN comprises: flowing a nitrogen precursor gas through afirst of the injector tubes; and while flowing the nitrogen precursorgas, flowing a plurality of separate pulses of a titanium precursor gasthrough a second of the injector tubes.
 15. The method of claim 9,wherein depositing TiN comprises flowing nitrogen and titanium precursorgases in accordance with a cycle comprising the following steps: flowinga pulse of the nitrogen precursor gas through a first of the injectortubes during a first time interval; flowing a pulse of the titaniumprecursor gas through a second of the injector tubes during the firsttime interval; and flowing a pulse of the nitrogen precursor gas throughthe first injector tube during a second time interval after the firsttime interval, wherein the titanium precursor gas is not delivered tothe processing chamber during the second time interval.
 16. The methodof claim 15, wherein the cycle further includes the following steps:temporally between the first and second time intervals, one of (1)purging the processing chamber with a purge gas and (2) evacuating theprocessing chamber; and temporally after the second time interval, oneof (1) purging the processing chamber with the purge gas and (2)evacuating the processing chamber.
 17. The method of claim 15, whereinthe titanium precursor gas comprises titanium tetrachloride (TiCl₄), andthe nitrogen precursor gas comprises ammonia (NH₃).
 18. An apparatuscomprising: a processing chamber configured to contain a plurality ofsemiconductor wafers; a titanium precursor source connected to thechamber to deliver a vapor of the titanium precursor into the chamber; anitrogen precursor source connected to the chamber to deliver a vapor ofthe nitrogen precursor into the chamber; a silicon precursor sourceconnected to the chamber to deliver a vapor of the silicon precursorinto the chamber; and a valve system configured to allow selectivecontrol of delivery of the vapors into the chamber.
 19. The apparatus ofclaim 18, wherein the titanium precursor comprises titaniumtetrachloride (TiCl₄), the nitrogen precursor comprises ammonia (NH₃),and the silicon precursor source comprises trisilane (Si₃H₈).
 20. Theapparatus of claim 18, further comprising a deposition control systemconfigured to control the valve system and temperature inside thechamber, the deposition control system programmed to deliver all of theprecursor vapors into the chamber at temperatures within about 100° C.of one another.
 21. The apparatus of claim 20, wherein the depositioncontrol system is programmed to deliver all of the precursor vapors intothe chamber at temperatures within about 50° C. of one another.
 22. Theapparatus of claim 18, further comprising a deposition control systemconfigured to control the valve system and temperature inside thechamber, the deposition control system programmed to deliver all of theprecursor vapors into the chamber at temperatures within about 400-550°C.
 23. The apparatus of claim 22, wherein the deposition control systemis programmed to deliver all of the precursor vapors into the chamber attemperatures within about 450-500° C.
 24. The apparatus of claim 18,further comprising a deposition control system configured to control thevalve system and programmed to deliver into the chamber alternatingpulses of the titanium precursor vapor and the nitrogen precursor vapor.25. The apparatus of claim 24, wherein the deposition control system isfurther programmed to, temporally between the alternating pulses of thetitanium precursor vapor and the nitrogen precursor vapor, either purgethe chamber with a purge gas or substantially evacuate the chamber. 26.The apparatus of claim 18, further comprising a deposition controlsystem configured to control the valve system and programmed to deliverinto the chamber a substantially constant flow of the nitrogen precursorvapor and a series of pulses of the titanium precursor vapor during theflow of the nitrogen precursor vapor.
 27. The apparatus of claim 18,further comprising a deposition control system configured to control thevalve system and programmed to deliver the precursor vapors into thechamber in multiple cycles of the following sequence: substantiallysimultaneous pulses of the titanium and nitrogen precursor vapors; andafter the simultaneous pulses, an additional pulse of the nitrogenprecursor vapor.
 28. The apparatus of claim 27, wherein the depositioncontrol system is further programmed to, in each cycle of the sequence:either purge the chamber with a purge gas or substantially evacuate thechamber after the simultaneous pulses and before the additional pulse;and either purge the chamber with a purge gas or substantially evacuatethe chamber after the additional pulse and before a next cycle of thesequence.
 29. The apparatus of claim 18, further comprising: a waferboat inside the processing chamber, the boat configured to support astack of spaced apart wafers that are generally parallel to one another;and a plurality of gas injector tubes each positioned within theprocessing chamber and oriented substantially perpendicular to thewafers, each injector tube extending along a majority of a length of thestack of wafers, each tube having a plurality of gas injector holesalong its length, each of the injector tubes being in fluidcommunication with one of the precursor sources to deliver one of theprecursor vapors into the reaction chamber.